In recent years, surface plasmons have been gaining popularity in various fields such as light source devices and sensing devices (refer to Patent Literatures 1 to 3 and Non-Patent Literatures 1 and 2). Surface plasmons are a group of free electrons that vibrate in a metal. Surface plasmons are excited on a metal surface an interaction with light.
The inventors of the present patent application have proposed plasmon coupling and emitting devices that are optical devices using surface plasmons in Japanese Patent Application No. 2009-227331 and Japanese Patent Application No. 2010-047944 (they were not disclosed when applied) so as to provide light source devices having high luminance and high directivity.
In a plasmon coupling and emitting device, a phosphor layer, a metal layer, and an exit layer are successively laminated. In the phosphor layer, incident light emitted from a light emitting device causes fluorescence to occur. The fluorescence couples with free electrons that are contained in a metal layer. As a result, surface plasmons are excited on the metal surface. In the exit layer, the surface plasmons are converted into light having a predetermined exit angle. The light having a predetermined exit angle is emitted from the exit layer.
In the related art references as disclosed in the foregoing Japanese Patent Application No. 2009-227331 and Japanese Patent Application No. 2010-047944, the dielectric constants of the carrier generation layer and the exit layer are adjusted so as to improve the coupling efficiency of fluorescence and surface plasmons. As a result, the efficiency and luminance for a plasmon coupling and emitting device are highly improved.